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Windscreen Repair or Replacement: Know the difference

Written by Oliver

Allow us to guide you in understanding the specific windscreen situation you’re dealing with. Are you facing a minor windscreen repair, or is it time for a complete screen replacement? Read on to learn more.

Spiderweb stone chip crack on windscreen

As you drive along, immersed in your daily commute, the sudden, unmistakable sound of a stone striking your car’s windscreen leaves you shocked – a moment instantly filling any car owner with apprehension.

Does this sound familiar? It’s likely why you’re here, seeking answers to your situation.

You pull over and examine your windscreen, discovering a small chip. You understand that if left unattended, it could gradually develop into cracks that spread further across the glass.

In this situation, you face uncertainty – how can you determine whether the damage is suitable for repair with resin or if a complete windscreen replacement is necessary?

It’s a common dilemma many car owners encounter when confronted with windscreen damage.

Our blog post provides clarity and guidance. We will explore the factors determining whether a repair is feasible or a complete windscreen replacement becomes imperative.

Let’s begin by understanding the windscreen’s construction and the reasons certain damages call for specific solutions.


Your Windscreen: Three Layers

The windscreen consists of three layers: two sheets of regular glass with an inner layer of plastic known as Polyvinyl Butyral (PVB) consolidated between the two pieces under high pressure.

This lamination layer serves a crucial safety function by holding the broken outer panes of glass together in the event of an accident, protecting the car’s occupants by preventing dangerous glass shards from dispersing into the cabin.

Typically, the damage doesn’t penetrate through all three layers when a stone or debris strikes the windscreen, unlike the picture below.

This design significantly simplifies the process of making minor repairs, ensuring the structural integrity of the windscreen while addressing the damage effectively.

Windscreen glass, a cross section showcasing the lamination in the middle.
Impact damage on a windscreen where all three glass layers has been penetrated.

Assess the windscreen damage

Fortunately, most minor chips and cracks are repairable without needing to replace the entire windscreen. When assessing the damage, it’s important to consider four factors:

  • Type
  • Size
  • Depth
  • Location


There are many different types of cracks, depending on what caused the damage and the speed at which it hit. Some are fixable,  others not.


This circular crack has a clean centre break and usually happens when a round object (e.g., stone) hits the windscreen. If caught in time, it is easy to fix bullseye cracks, and it typically doesn’t require a complete windscreen replacement.

Half Moon

This crack is half a bullseye, often has a dull edge, and is easily repairable.

Edge Crack

Edge cracks are the most common. They start close to the edge of a windscreen and tend to move inward over time. The windshield will need replacement if the damage is flush with the frame or longer than a few inches.

Floater Crack

Floater cracks tend to occur in the middle of the windscreen and often obstruct the driver’s view. The crack lines spread quickly and usually requires total windscreen replacement.

Star Break

Star breaks start with an impact hole with one or two small cracks leading outward. These cracks tend to grow and spread. It is easily repairable, while the star is small and debris-free.

Combo Break

Combination breaks are mostly the result of serious damage, such as an accident or severe impact to the windscreen (e.g., falling rocks and branches). Due to the sheer of number chips and cracks, replacing the windscreen is the more affordable option.


Most auto glass repair technicians will be able to repair chips that are less than 1 inch in diameter (or about the size of a £2 coin), and cracks that are no longer than 3 inches.


If the chip or crack has gone through all three layers of glass, it likely is unfixable. Even if it is just a small hole, it will be an area of weakness that undermines the strength of the entire windscreen.


Chips and cracks in the driver’s line of sight require a complete windscreen replacement. No matter how good the repair job is, there may still be some mistiness, discolouration, or unevenness which can distract the driver. It will also result in MOT failure – something you certainly don’t need.

Damage near the windscreen’s edge (where it meets the metal frame) is also an essential consideration. Even a minor crack in this position will weaken the integrity of the windscreen and compromise your safety.

This is because part of the crack or chip may be out of sight beneath the frame and impossible to repair safely.

Anything closer than 7cm to the edge will require a windscreen replacement.

windscreen rain sensor closeup

Can the windscreen repair or replacement wait?

There are many reasons why you should repair windscreen chips and cracks as soon as possible.

Cracks lengthen quicker than you think. One day you have a tiny chip, and next, there’s a long crack along your windscreen. It could mean the difference between an affordable chip repair and an expensive glass replacement.

In addition, dust and moisture settle in the nooks and crannies of a crack over time and cause further damage.

Finally, and most importantly, a chipped or cracked windscreen is a safety concern. Even tiny imperfections compromise the integrity of the glass.

A cracked or chipped windscreen can result in an instant MOT failure. It is dependent mainly on the position and extent of the damage.

For MOT purposes, it’s important to distinguish between the different zones of the windscreen.

The A zone is a 290mm wide section directly in front of the driver (in line with the steering wheel). No damage is allowed in this area. Some say you can try to get away with tiny chips up to 10mm big, but even these small imperfections often result in an MOT fail.

The B zone is the remaining section on the driver’s side. You can see how far this extends by putting on the windscreen wipers – the area the wipers sweep is the B zone. Damage up to 15mm wide (the size of a five pence coin) is allowed in this zone.

The C zone consists of the area the wipers sweep on the passenger side. Damage here can extend up to 25mm.

The D zone includes the rest of the windscreen. Chips or cracks up to 40mm are legal, but anything larger, and you’ll need to replace the windscreen to ensure a roadworthy pass.

Windscreen Repair or Replacement - Choices and Options.

Windscreen repair vs replacement: Important Facts

  • windscreen replacement is more expensive and takes more time than windscreen repair.
  • Most minor chips and cracks take under an hour to repair. A windscreen replacement takes a few hours.
  • Remember, the key is to sort out the crack as soon as possible. The longer you leave it, the higher the chances of the damage spreading and requiring a full windscreen replacement.
  • Windscreens are responsible for around 30% of the car’s structural integrity. An incorrectly fitted windscreen, or one with too many shoddy repair jobs, can have dangerous results in the event of an accident.
  • Windscreens are a vital component of airbag technology. A weak, damaged, or incorrectly fitted windscreen can detach when an airbag deploys. It will then inflate over the dashboard instead of protecting the occupant.
  • If you’ve repaired chips on your windscreen more than eight times, you’ll need a total windscreen replacement.


Republished on April 3, 2023 - Originally published on April 15, 2022


Oliver, our astute business developer, is the mastermind behind the success of UK Car Glass. His visionary approach and strategic acumen have sculpted the brand's prominence within the UK and have been pivotal in its expansion to other countries. With an innate ability to identify opportunities and craft innovative solutions, Oliver's leadership has been instrumental in establishing UK Car Glass as a renowned name in the industry. His commitment to excellence and growth is reflected in every facet of the business, ensuring that the brand continues to set benchmarks on an international scale.


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